Mobile homes, pulled by specially designed (设计) trucks have been increasing in numbers all over the United States. Often, driving along, you can see some mobile homes high on a hill. Some stand under trees along a river or a lake. They're wonderfully built homes. Sometimes they're as much as 40 feet long, with two to five rooms, and you can find many things you need in them. When you park your mobile home, water, electricity power and telephones are connected, and you can enjoy yourself there.
      The fact that these homes can be moved doesn't mean that they do move all the time. Sometimes their owners stay for years in one place, plant gardens, build walls and so on. These homes are often quite expensive. Some even cost $ 20,000.
      Why does a family choose to live in such a home? Well, it's comfortable, easy to keep clean, easy to keep warm, no need to paint. What's more, the fast increase of mobile homes in numbers has something to do with the job uncertainty(不稳定性). Nobody knows what will happen tomorrow. If a factory closes down, you may be trapped with the house you can't sell. However, if you have a mobile home, you can move on easily.
      The greatest selling attraction of these mobile homes is that they can be improved every year. If you're doing well, you may change a new model just as you do with a car. There is a ready market for used ones, so the price of the mobile homes is higher than that of automobiles (汽车).
56. Which of the following may NOT attract（吸引）people to buy mobile homes?
    A. The new model appears every year. 

B. Walls can be easily built around them.
   C. They don't need to be painted.        

55. What would be the best title for the text?

   A. How to protect your eyes.

   B. How to protect your hands and wrists.

   C. How to use a computer safely.

   D. How to protect your back.

（C）

54. Your eyes and hands will be safe if__________.

    A. you work near a window

    B. you often take rests from working

    C. you use a keyboard for a long time

D. the window is behind you

53. Hand and wrist injuries can happen when you __________.

   A. get plenty of exercise

   B. move in the same way again and again

   C. rest your wrists on something

   D. keep your elbows as high as the keyboard

52. A computer screen may injure your eyes if __________.

   A. you sit 60 centimeters away

   B. you remember to look away

   C. your eyes are too close to it

   D. the window is on your left or right